HLA typing was performed on lymphocytes from patients with a common disease or from families where more than one individual had a common disease type. HLA typing was performed in a cohort of individuals with AIDS, either Kaposi's sarcoma or opportunistic infections or individuals at risk for this disease. A total of 250 individuals have been HLA typed. These patients have been followed over a 3-year period. The objectives of these studies are to examine possible genetic susceptibility to the development of AIDS or AIDS-related complex that is related to expression of histocompatibility antigens. Increases in HLA-A3, AW 23, and Cw 4 were found in patients who developed Kaposi's sarcoma compared to other groups tested. HLA-B8 and DR3 were decreased in frequency and patients with Kaposi's sarcoma were compared to other HTLV-III seropositive individuals. HLA typing was performed in 11 families with hereditary cutaneous malignant melanoma and dysplastic nevi in order to determine if susceptibility was genetically linked to the major histocompatibility complex. No linkage was found. This data is in contrast to previous reports of family studies where it was suggested that the development of melanoma was related to HLA antigens. HLA typing was performed on families where more than one individual had Hodgkin's disease. These studies show a high degree of correlation between the presence of HLA DQ1 antigen homozygosity in individuals who have the disease. These studies suggest the possibility that this locus contributes to the development of this malignancy.